The invention relates to electrostatic dust precipitators. Electrostatic dust precipitators have been used in many plants and factories where dust causes polution of the atmosphere, and injuries the health of workmen and where clean environments are required.
FIG. 1 shows one example of the prior art electrostatic dust precipitator comprising a plurality of spaced apart metal rods 1 and a plurality of parallel equally spaced metal wires or discharge electrodes 3 suspending from the metal rods 1. Weights 2 are connected to the lower ends of respective discharge electrodes 3 to maintain them in vertical positions. Dust collection electrodes in the form of flat metal plates 4 are disposed between and outside the arrays of discharge electrodes 3. The weights 2 serve to maintain the distance between the metal wires 3 and the metal plates 4 at a constant value.
In operation, a negative voltage is impressed upon the metal wires 3 and a positive voltage is impressed upon the metal plates 4. Gas or air containing dust is passed between the metal plates 4 in the direction indicated by an arrow. Between the metal wires 3 and the metal plates 4 is created a corona discharge to ionize the gas or air. Most of the particles of the dust are charged negatively and attracted by the positively charged metal plates. However, some of the particles are charged to the opposite polarity so that they are attracted by the metal wires 3. For this reason, after the precipitator has operated for a long period, sufficient amount of corona discharge cannot be produced, thereby decreasing the efficiency of operation. Accordingly, the metal wires are hammered from time to time for removing the dust collected thereon. This not only requires to provide hammers but also causes breakage and short circuiting of the metal wires.
Another example of the prior art electrostatic dust precipitator is shown in FIG. 2 which comprises a plurality of flat plate shaped dust collecting electrodes 41 and a plurality of flat plate shaped discharge electrodes 42 which are interleaved in spaced parallel relationship. A plurality of needles 43 are secured to the inlet side of each discharge electrode 42. The electrostatic dust precipitator shown in FIG. 2 operates in the same manner as that shown in FIG. 1. With this construction, however, the intensity of electric field decreases toward the center of the dust collecting electrodes 41 so that most of the dust is collected on the surface portions of the dust collecting electrodes 41 and on the discharge electrodes 42 near the needles 43 so that even when large electrodes are used, the entire surfaces are not used thus decreasing the efficiency of dust collection. For this reason, in order to treat a large volume of dust containing gas it has been necessary to use a large and expensive electrostatic dust collector.
In the electrostatic dust precipitator of the type referred to above it is essential to maintain constant the electrode spacing. Otherwise, the corona discharge concentrates at some portions or sparks are formed thereby greatly decreasing the efficiency of dust collection. Further, when plate shaped electrodes are used it is difficult to manufacture and install them in perfect parallel positions, that is with uniform spacings. Since large plate shaped electrodes are prepared from rolled metal plates, due to the stress and strains thereof it is difficult to install them perfectly flat. Further, plate shaped electrodes are greatly deformed due to the heat strain created therein during operation. This also decreases the operating efficiency. Flat plate shaped electrodes will be readily deformed by external forces applied thereto at right angles. Thus, when an intense electric field is established between the electrodes they will be deformed greatly.
For the reason described above, it is extremely difficult to maintain uniform distance between the plate shaped electrodes over the entire surfaces thereof so that at present a large error allowance is permitted, thus greatly decreasing the actual dust collecting efficiency than the theoretical value.